1. Field of the Invention
The invention relates to a television (TV) receiver comprising a radio frequency (RF) section, a mixer stage to which a tuning frequency is applied from a tuning oscillator, an intermediate frequency (IF) section, a synchronous detection device and a frequency and phase-locked loop (FPLL) circuit which comprises a phase-locked loop (PLL) and a frequency-locked loop (FLL), said IF section being coupled to a phase detector of the PLL and to a frequency detection device of the FLL, said phase detector and frequency detection device being commonly coupled to a loop branch having the two loops in common and incorporating a loop filter and a controllable oscillator, said controllable oscillator applying a local in-phase carrier to the synchronous detection device and a local phase quadrature carrier, to the phase detector.
2. Description of the Related Art
A TV receiver of this type is known from the article "Modular video IF concept" by M. Huber et al. published in IEEE Transactions on CE, Vol. CE-29, No. 3, Aug. 1983, pp. 414-418.
In the mixer stage of the known TV receiver, a desired RF TV reception signal is converted into a TV IF signal by means of a suitably chosen tuning frequency. In the synchronous detection device, the TV IF signal is synchronously detected, which results in a baseband TV signal. The local synchronous IF detection carrier required for synchronous detection and hereinafter briefly referred to as the local IF carrier is obtained by means of a controllable oscillator incorporated in a PLL. For a correct synchronous detection the local IF carrier should be equal in frequency and phase to the IF carrier frequency of the received TV signal, hereinafter briefly referred to as the actual IF carrier frequency. In practice this requirement means that the PLL should have a comparatively narrow band.
Consequently, the capture range of the PLL is too small to realize an acceptable tuning behavior as such. To improve the tuning behavior, the PLL in the known TV receiver is combined with an FLL, making common use of the loop filter and the controllable oscillator so that the FLL acts on the controllable oscillator of the PLL via the loop filter. The capture range of the FLL is to be chosen considerably larger than that of the PLL. Due to the combined frequency and phase control.,this loop combination is also referred to as frequency and phase-locked loop (FPLL).
The FPLL is mainly employed to establish a frequency and phase synchronization of the local IF carrier on the actual IF carrier. In the case of frequency deviations between the local and actual IF carriers within the capture range of the FLL, the FLL brings the frequency of the local IF carrier sufficiently close to that of the actual IF carrier so as to enable the PLL to lock in. The PLL subsequently realizes a phase synchronization between the actual and the local IF carrier.
For a correct signal processing, notably in the IF section, the actual IF carrier frequency should also be equal to the intermediate frequency to which the IF section is tuned, hereinafter briefly referred to as the correct intermediate frequency. To this end the frequency of the tuning oscillator is to be controlled at a value by which the intermediate frequency deviates from the carrier frequency of the desired RF TV reception signal. A realization of such a control is not shown in said article.